Kinases are a superfamily of enzymes that transfer a phosphate group from ATP to target proteins. There are more than 518 kinases encoded in the human genome, including 90 tyrosine kinases, 388 serine/threnine kinases and 40 atypical kinases (Manning, G., et al., Science, 2002, 298(5600): 1912-1934). They play vital roles in cell activation, proliferation, differentiation, migration, vascular permeability, and so on. Dysfunction of kinases has been implicated in various diseases such as cancer, inflammation, cardiovascular diseases, diabetes, and neuronal disorders. Several kinase inhibitors have been developed for the treatment of cancers, including but not limited to imatinib, dasatinib, nilotinib, gefitinib, erlotinib, lapatinib, sunitinib, sorafenib, pazopanib, evrolimus, trastuzumab, cetuximab, panitumumab, and bevacizumab (Knight, Z. A., et al., Nat. Rev. Cancer, 2010, 10(2): 130-137).
BRAF is a member of the Raf kinase family of serine/threonine-specific protein kinases. BRAF plays an important role in regulating the MAPK/ERK signaling pathway, which affects cell division, proliferation, differentiation, and secretion. The RAS/RAF/MEK/ERK pathway acts as a signal transducer to send extracellular signals such as hormones, cytokines, and various growth factors into cell nucleus, directing a range of biochemical and physiological processes including cell differentiation, proliferation, growth, and apoptosis (McCubrey, J. A., et al., Biochim. Biophys. Acta, 2007, 1773 (8): 1263-84). The RAS/RAF/MEK/ERK pathway is frequently mutated in many human cancers (Downward, J., Nat. Rev. Cancer, 2003, 3 (1): 11-22). The finding that mutations in BRAF caused a wide range of human cancers and many of these tumors are dependent on the constitutive activation of BRAF/MEK/ERK pathway fueled drug discovery efforts in searching for small molecule inhibitors targeting BRAF mutants (especially the most common form of BRAFV600E) (Davies, H., et al., Nature, 2002, 417: 949-954) (Flaherty, K. T., et al., New Engl. J. Med., 2010, 363: 809-819). It was found that BRAF mutations are responsible for more than 50% of malignant melanomas, ˜45% of papillary thyroid cancer, 10% of colorectal cancers, and had also been identified in ovarian, breast, and lung cancers (Cantwell-Dorris, E. R., et al., Molecular Cancer Therapy, 2011, 10: 385-394). Recently it was reported that almost all hairy-cell leukemia patients carry BRAFV600E mutation and inhibition of the enzyme caused significant remission of the disease (Sascha, D., et al., New Engl. J. Med., 2012, 366:2038-2040). BRAF-specific inhibitors such as Vemurafenib (RG7204), PLX-4720, GDC-0879, and Dabrofenib (GSK2118436) have been reported to be efficacious in causing tumor regression in both preclinical and clinical studies (Flaherty, K. T., et al., New Engl. J. Med., 2010, 363: 809-819; Kefford, R. A., et al., J. Clin. Oncol., 2010, 28: 15s).
Accordingly, the identification and development of small-molecules that specifically modulate BRAFV600E kinase activity will serve as therapeutic approaches for successful treatment of a variety of BRAFV600E kinase-related diseases or disorders, such as cancers.